1. Field of the Invention
This invention relates to a refrigerant expansion device, and more particularly, to a refrigerant expansion device adaptable to a refrigeration cycle which controls the expansion valve of refrigerant flowing to a low pressure portion from a high pressure portion, and controls the flow rate of a refrigerant.
2. Description of the Prior Art
Generally, a refrigeration cycle is mainly comprised of a compressor, an evaporator, a condenser, and a refrigerant expansion device. A refrigerant under low pressure is compressed in the compressor. The refrigerant under high pressure enters into the condenser where it condenses. The refrigerant discharged from the refrigerant expansion device is expanded in the refrigerant expansion device to create a low pressure situation. Subsequently, the refrigerant is heat exchanged in the evaporator with the surrounding air.
There is a modified refrigeration cycle which performs in either refrigerating mode or heating mode. In this cycle, a 4-way valve determines the refrigerant is directed into either the indoor heat-exchanger or the outdoor heat-exchanger. This accomplishes the various functions of the refrigeration cycle. Further, the flow rate of the refrigerant being discharged can be controlled by the variation of the frequency of the compressor.
In this refrigeration cycle, the refrigerant expansion device performs a major function. The refrigerant expansion device enables the entering refrigerant to expand as the low pressure refrigerant, and the entrance of liquid refrigerant into the compressor is avoided. Further, the expansion device performs such that evaporated refrigerant at excessive temperature is prevented from entering into the compressor. Furthermore, the expansion device also sends to control the flow rate of refrigerant such that the expansion of the refrigerant entering from the condenser can be controlled.
There are three main types of refrigerant expansion devices commonly used: an electronic expansion valve, a capillary tube, and an orifice. The electronic expansion valve is a device whereby the temperature of refrigerant in the evaporator is detected and the flow rate of the refrigerant entering into the evaporator is controlled. The operation of the electronic expansion valve is performed by a variable passage in a needle valve inside the valve body. This device exhibits the high effect in the expansion of the refrigerant and the control of the flow rate of the refrigerant. However, the cost of the device is very high, and its structure is very complex. Furthermore, If the point of the temperature detection is far enough away, accurate detection can not be obtained.
In a capillary tube type device, even though the cost is much lower and it is very easy to manufacture, the installation work is very inconvenient because it is made with a 1 meter length of small diameter tube. In addition, since the flow rate of the discharged refrigerant is controlled in accordance with the varied frequencies of the compressor, there is a limit in the control of the refrigerating capacity of the refrigeration cycle. Moreover, the refrigerant is accelerated at the outlet of the capillary tube almost to the speed of sound(maximum permissible speed). Thus, the flow rate of the refrigerant under a high pressure reaches a limit when passing through the capillary tube.
In other words, as the RPM of the compressor increases, the flow rate of the discharged refrigerant is increased. However, the flow rate of the refrigerant which expands through the capillary tube and flows to the condenser cannot be increased anymore. The refrigerant which is not discharged from the capillary tube, remains at the outlet of the condenser, and a lack of refrigerant occurs in the evaporator. This contributes to a poor refrigerating capacity and low electrical efficiency for this refrigeration cycle.
When the compressor is operating at low RPM, the flow rate of the refrigerant discharged from the compressor is reduced. In the capillary tube, the flow rate of the refrigerant can not be controlled properly. Much more refrigerant than needed by the evaporator remains, thereby contributing poor capacity and low electrical efficiency for the refrigeration cycle.
For the above reasons, concentration on development of an inexpensive and simple refrigerant expansion device has been taking place.
One of the resulting devices is U.S. Pat. No. 5,134,860 issued on Aug. 4, 1992, and called `variable area refrigerant expansion device having a flexible orifice for heating mode of a heat pump`. This device is comprised of an expansion chamber having an orifice passage for expanding the refrigerant, an intake opening at the inlet portion of the expanding chamber operated when in heating mode, and a check valve at the inlet portion of the expanding chamber operated when in cooling mode. The check valve is for preventing the return of the refrigerant. The orifice passage is made of flexible material and this expands or contracts according to the pressure of the refrigerant, thus controlling the flow rate of refrigerant discharged. When in heating mode, the refrigerant is taken in through the inlet opening and the check valve is in an opened position. The non-changed refrigerant flows through the expansion device. The expansion device is situated facing each direction between the indoor heat-exchanger and the outdoor heat-exchanger. Using this system, the heating mode, cooling mode, and the flow rate control mode are all accomplished simultaneously. If need be, only the heating mode or the heating and cooling mode can be utilized.
However, the expansion device needs a durable orifice tube which is made from an expandable material even at high temperatures. Moreover, an additional check valve is provided, so its manufacture and assembly is too complex and its cost is very high relation to a conventional capillary tube. As the pressure of the refrigerant taken in is increased, the orifice tube expands to increase the flow rate of the discharged refrigerant. This creates a problem with the relative expansion of the orifice passage contributing to poor expansion efficiency of the refrigerant.